The present invention generally relates to an internal power voltage generator, and more specifically, to an internal power voltage generator of a current mirror type which converts an external power voltage into an internal power voltage by using a reference voltage. The internal power voltage generator generates a predetermined reference voltage by making use of an external power voltage during a specific power potential period, but generates the predetermined reference voltage by making use of the internal power voltage after the specific power potential period.
Semiconductor integrated circuits need to be operable with lower power consumption and to be hardly affected from external noises, accompanying with enhancement of reliability and stable operations thereof.
In view of the above basic requirements, in order to drive internal circuits at stable operation states, it is customary to use an internal power voltage made in the semiconductor integrated circuits rather than an external power voltage dependent on external circumstances.
There are various ways for generating a stable internal power voltage. FIG. 1 illustrates a conventional voltage down converter of a current mirror type in which an external power voltage VEXT is converted into a conventional internal power voltage QVint by using a reference voltage.
The conventional voltage down converter usually comprises a differential amplifier. The first reference circuit 1 receives the external power voltage VEXT and generates the first reference voltage Vr1. The first reference voltage Vr1 is potential-amplified by the second reference circuit 2. The second reference circuit 2 generates the second reference voltage Vr2.
A stress voltage circuit 3 loads a stress voltage on the second reference voltage Vr2. An internal power driver 4 generates the internal power voltage QVint with reference to output an voltage from the stress voltage circuit 3. The internal power voltage QVint is provided to an internal circuit 5.
However, since the first reference circuit 1 of the conventional voltage down converter utilizes only the external power voltage VEXT as a power source, the first reference voltage Vr1 may change when the external power voltage VEXT fluctuates due to external environments.
In other words, in the conventional voltage down converter, the external power voltage VEXT applied to the first reference circuit 1 may be easily variable in accordance with external temperature changes or noises. Accordingly, in special cases, the external power voltage VEXT of sufficient potential may be transferred to the current mirror loop in the voltage down converter. As a result, it would be difficult to obtain a reliable value of the first reference voltage Vr1.
It is, therefore, an object of the present invention to overcome the above problems encountered in the prior art and to achieve stable operation of a semiconductor device by selectively utilizing external or internal power voltages in accordance with an operation power potential period of the semiconductor device.
According to an aspect of the present invention, there is provided an internal power voltage generating unit including: a switch control means for connecting an external power voltage terminal to a internal power voltage supply line in an operation power potential range, and for cutting off the connection between the external power voltage terminal and the internal power voltage supply line if the external power voltage reaches a predetermined potential level; a first reference circuit for generating a predetermined first reference voltage by making the use of the internal power voltage; a second reference circuit for generating a second reference voltage by amplifying the first reference voltage supplied from the first reference circuit; and an internal power driver for generating the internal power voltage with the second reference voltage supplied from the second reference circuit, and for driving internal circuits with the internal power voltage.
The foregoing features and advantages of the invention will be more fully described in the accompanying drawings.